Diffuse reflectance flash photolysis

Abstract

Examples are given demonstrating recent progress which allows flash photolysis investigations of opaque materials by using diffuse reflectance from analysing sources for transient detection. Experimental details of a nanosecond diffuse reflectance laser flash photolysis system are presented. The limitations associated with the use of integrating spheres for collecting the analysing light are discussed. The decay of transient absorption and time-resolved spectra are reported for triplet states in microcrystals (benzil), adsorbed as a fraction of a monolayer on powdered silica (acridine) and dyed on cotton fabric (aluminium sulphonated phthalocyanine). Photoinduced changes in diffuse reflectance of Co-doped ZnO are also reported and tentatively assigned. The relationship between the measured changes in diffuse reflectance and the distribution of transients below the irradiated surface is discussed and equations which can be applied in two limiting cases are given. Finally, the first observation of a transient absorption on the picosecond timescale from an opaque sample is presented. The potential of the technique for studying the mechanism of heterogeneous photoreactions is stressed.